SALT LAKE CITY (Reuters Health) - Just because water comes in
a bottle doesn't mean it's sterile, according to an expert who
spoke here Tuesday at the American Society for Microbiology's
annual meeting.

"There is a misconception that bottled water is free from microbes.
It is not," said Dr. Fred Rosenberg of California Lutheran University
in Thousand Oaks. But, he added, "If you are a healthy individual,
there's probably little to fear from it."

However, it is not a great idea to share bottled water after
it has been opened, or to leave an open bottle sitting around
in warm weather for too long, Rosenberg told Reuters Health.

While there haven't been widespread outbreaks of illness linked
to consumption of contaminated bottled water, Rosenberg said,
bottled water can indeed contain microbes at levels capable of
making a person with a weak immune system sick. Bacteria may come
from the water source, or can be introduced during the bottling
process.

The US does not monitor bottled water for the presence of Pseudomonas
aeruginosa, which can cause illness, is often resistant to antibiotics
and is a reliable indicator that contamination has occurred during
bottling, according to Rosenberg.

The US Food and Drug Administration (FDA) has said such testing
would be too expensive, he noted, but both Europe and Canada monitor
bottled water for this bug.

The FDA does watch bottled water for contamination with coliform
bacteria. But standards for municipal water--which is monitored
by the Environmental Protection Agency (EPA)--are actually tougher.
While the FDA allows for the presence of tiny amounts of coliform
bacteria in 1 out of 10 bottles tested, the EPA has zero tolerance.

Glass bottles, the researcher said, are less hospitable to growth
of bacteria than plastic ones. And the organism that causes cholera
can survive in flat bottled water, but dies off in carbonated
water within a day.

As bottled water is capable of harboring "medically important"
microbes, Rosenberg stressed that "frequent analysis and stringent
regulation are crucial to maintaining human health."